1. Field of the Invention
The present invention relates to the field of flexible hose and in particular relates to a vacuum hose and method for making the hose from spirally wound, flexible strips and in particular to vacuum hose which is assembled from strips which have differing characteristics.
2. Description of the Prior Art
Flexible hose, such as typically used in vacuum hose applications, must be characterized by a high hoop strength, great flexibility and high resistance to abrasion and collapse from kinking or sharp bends. Prior art hoses have been able to achieve some of these characteristics only at the expense of other characteristics.
For example, flexible hose has traditionally been made of a flexible material, such as plastic reinforced by steel wire to give it the required hoop strength. See for example Swan, "Flexible Tube", U.S. Pat. No. 3,273,600; Haren, "Hose and Method of Manufacture", Canadian Pat. No. 800,406; and Richitelli et al., "Wire-Reinforced Helically Fabricated Flexible Conduit", U.S. Pat. No. 3,323,553.
Later, steel reinforcing wire was replaced by a plastic wire which was thicker than the steel wire in order to obtain the required structural rigidity. Since the plastic wire required a much larger mass, various plastic, corrugated hoses have been devised. See, Hawerkamp, "Method of Making Continuous Corrugated Plastic Pipe", U.S. Pat. No. 3,477,891; Osborn, "Method of Making Corrugated Flexible Hose", U.S. Pat. No. 3,445,308; D'Onofrio, "Method for Forming a Helically Corrugated Concentric Tubing Unit", U.S. Pat. No. 3,777,343. However, in order to achieve the required flexibility, many of these corrugated pipes have sacrificed strength and tend to collapse or kink at sharp bends. Moreover, hose of a corrugated nature or having plastic wire for hoop strength often has the flexible membrane of the hose at the top of the crown or the exterior surface of the hose. As a result, the most vulnerable part of the hose is subjected to abrasion or puncture. Any attempt to increase the thickness, toughness or hardness of the membrane portion of the hose also reduces the flexibility of the hose. Some flexible, prior art hoses which have sufficient toughness to avoid puncture or abrasion also have the feel of rigid pipe.
To improve abrasion resistance and durability, various interlocking helical designs have been devised for flexible hose. A strip is configured such that it may be helically wrapped and each adjacent wrap bound to the adjoining wrap to form a sealed, cylindrical tube. Sealing by an adhesive or thermoplastic material normally leaves the sealed joint rigid. The flexibility of the hose is then attributed to the innerlying membrane between adjacent seals. See for example Squirrell, "Flexible Hose of Interlocking Helical Convolutions", U.S. Pat. No. 3,255,780; and Lykle, "Flexible and Extensible Hose", U.S. Pat. No. 3,542,078. However, each of these prior art structures sacrifice flexibility for durability or necessitated a complex structure which could be fabricated and sealed only with substantial difficulty or expense.
What is needed is a reliable, long-lived flexible hose construction which does not require an excessive amount of material, which is inexpensive to manufacture, which can be made of various substances, which can be simple in design, which is lightweight, which can be easily fabricated, which has high hoop strength, which is highly resistant to abrasion and yet maintains extreme flexibility without any tendency to collapse or kink on sharp bends.